CheckIndex is great for testing and when tracking down lucene bugs.
But in cases where users just want to verify their index files are OK, it is very slow and expensive.
I think we should add a -fast option, that only opens the reader and calls checkIntegrity(). This means all files are the correct files (identifiers match) and have the correct CRC32 checksums.
For our 10M doc wikipedia index, this is the difference between a 2 second check and a 2 minute check.